In successful commercial product line organizations, the number and diversity of products deployed can grow to be extremely large, partially due to the efficiencies made available from systems and software product line engineering (PLE) tools and methods. In market segments ranging from industrial pumps to automobiles, it is not unusual for companies to manufacture millions of product instances every year, in thousands of different “flavors.”
The extreme scale and scope of diversity in product lines of this size creates significant challenges to engineers implementing the product line, product marketers defining the space of available products, and customers selecting from available products. To provide order and clarity about their product groupings and offerings within this type of complex product space, companies often organize their products into a product family tree, thereby enabling their customers to effectively navigate among the huge number of offerings and to efficiently converge on a suitable product instance.
For example, an automotive manufacturer might hierarchically structure their entire product line portfolio with millions of instances into a family tree with 5 levels:                Platforms. A platform is a family of vehicles of similar size and structure that can be manufactured in the same assembly plant. Examples might be pickup trucks, large sedans, and small coupes.        Programs. A program is subfamily of vehicles within a single platform, known by consumers as the “model” and often found in nameplate display on the back of the vehicle.        Regional programs. A regional program is a subfamily of vehicles within a single program, manufactured for the legislative, geographic, climate, cultural, and marketing characteristics of a particular country.        Trim levels. A trim level is a subfamily of vehicles within a single regional program, representing different tiers of capabilities, accessories, and associated cost. Trim levels are marketed using terms such as base, standard, and luxury.        Vehicle instances. A vehicle instance is a subfamily member within a single regional program trim level. Characteristics of a vehicle instance are determined by the consumer-selectable options available on a particular trim level.        
In contrast to the way that the PLE community traditionally focuses on techniques for selecting and solving for features on a particular product instance, product line organization with large family trees expend most of their effort determining which features will not be available within a subfamily. As a result, those skilled in the art are often more focused on identifying the features that they don't want on a particular platform, program or trim package, than on specifying the features they actually want configured on any particular product instance.